Aspects of indirect amplification methods for atomic absorption spectrophotometry

A study has been made of indirect methods for arsenic and silicon based on molybdenum heteropoly acid chemistry with the final measurement by atomic absorption spectrometry. The optimum conditions for the formation and solvent extraction of the neteropoly acids were chosen to minimize the blank levels. Procedures have been developed for the determination of silicon and arsenic. Silicon is extracted as 12-molybdosilicic acid into a mixture of diethyl ether and pentan-l-ol (5+1). The coextraction of excess molybdate reagent is prevented by the addition of citrate which also destroys molybdophosphoric and molybdoarsenic acids. The organic layer is washed with dilute hydrochloric acid and determinations are made by using solution spectrophotometry and carbon rod electrothermal atomic absorption spectrometry. The method has been applied to the analysis of several British Chemical standard steels. Arsenic is extracted as 12-molybdoarsenic acid into a mixture of diethyl ether and pentan-l-ol(3+1). The interferences from other heteropoly forming elements could not be suppressed by the addition of masking agents. A method in which arsenic was converted to arsine, then oxidized to arsenate and finally determined after formation and extraction of the 12-molybdoarsenic acid was evaluated. The method was critically compared with the hydride generation atomic absorption method by analyzing several British Chemical standard steels. Various methods for determining molybdenum by electro-thermal atomizationwere investigated including the use of carbon rods (pyrolytically coated and uncoated), graphite tubes (coated and uncoated), L'vov platform and graphite tube treated with tantalum. Standard solutions were prepared from ammonium molybdate tetrahydrate and the atomization temperature was about 2800 degrees C. Comparisons were made on the basis of sensitivity, detection limit, precision, linear range and lifetime of the atomizer.